1. Field of the Invention
The present invention relates to an antivibration device intended to reduce the transmission of vibration between two bodies, and to applications of said antivibration device.
Although said antivibration device can be used in all situations in which transmission of vibration between two bodies needs to be reduced, it is more specifically applicable to improving a device for the suspension of a transmission gearbox of a rotary-wing aircraft and, in particular, of the main transmission gearbox of a helicopter.
2. Description of the Related Art
It is known that a helicopter main transmission gearbox of this type, mounted between propulsion means and a lift rotor of said helicopter so that it is roughly longitudinal with respect to the axis of said rotor and which is suspended from the fuselage of said helicopter, is subjected to significant vibration generated by said lift rotor. This vibration is particularly troublesome because, in the absence of any system to filter the vibration, such as a transmission gearbox suspension device for example, it is transmitted to the structure of the fuselage of the helicopter and in particular is likely to limit the maximum speed of the helicopter, structurally weaken it and have an adverse effect on the comfort of the occupants of the helicopter. It is therefore necessary for said suspension device to be as effective as possible in opposing the transmission of such vibration and the associated forces from the main transmission gearbox toward the fuselage of the helicopter so as to avoid premature wear of the elements subjected to this vibration and make the pilot cockpit and passenger cabin as comfortable as possible.
Patents FR-2 499 505 and FR-2 669 982 in the name of the Applicant Company, disclose helicopter main transmission gearbox suspension devices which allow a particularly efficient reduction in the vibration generated by the lift rotor.
To this end, the suspension devices described in these prior-art documents are of the type comprising:
support or attachment pieces or bars, distributed radially around said transmission gearbox, the upper ends of which pieces or bars are connected to the upper part of the transmission gearbox and the lower ends of which pieces or bars are articulated on suspension leaves or on the fuselage; PA1 possibly a suspension system connecting the lower part of the transmission gearbox to the aircraft fuselage and comprising, in particular, said suspension leaves which are distributed radially around said transmission gearbox in a plane which is roughly orthogonal to the axis of the rotor, the radially inner ends of which are fixed to the lower part of said transmission gearbox and the radially outer ends of which are articulated on the fuselage; and PA1 resonator means associated respectively with said support pieces, either at their lower ends (FR-2 499 505), or at their upper ends (FR-2 669 982). Each of said resonator means comprises a mass support which is secured by one of its ends either to the suspension leaf connected to the associated support piece or directly to this support piece, and which is equipped at its other end with a beating mass. Said resonator means are essentially intended to reduce the vibration of the rotor transmitted by said support pieces. PA1 its accessibility is limited and its size is large, particularly as a -result of the presence of the aforementioned resonator means; and PA1 its cost is high, particularly because of the existence of elastomer articulations, particularly to allow an effective arrangement and effective operation of the suspension leaves and of the mass supports. PA1 a first cylindrical chamber and a second cylindrical chamber which communicate, which are filled with a fluid and which are deformable in the direction of the vibrational movement. The second chamber has a cross section of smaller area than the first chamber so that this second chamber is deformed to a greater extent than the first and its fluid is accelerated when there is deformation; and PA1 an inertial mass which is connected to a piston arranged in said second chamber and which is moved when the vibration is generated, the movement of this inertial mass leading to a change in the pressure of the fluid in said second chamber so as to generate an effect which opposes the vibration. PA1 its operation is limited by the freezing point of the fluid used; PA1 there are risks of leakage of said fluid, liable in particular to reduce the effectiveness of said device; PA1 it is difficult to completely fill the device with fluid, because of the risk of the appearance of air pockets, without providing complex and expensive bleed means; and PA1 particularly because of the high number of parts of which it is made, it is particularly complicated and difficult to produce. PA1 an elastic annular element which is connected to said two bodies so as to serve as a connection between them and which is capable of being deformed under the action of vibration generated in at least one of said bodies; and PA1 a resonator means connected, via at least two leaves which are flexible in terms of bending and rigid in terms of tension and in terms of compression, to the internal face of said annular element so as to be set in oscillating rotation when said annular element is deformed, by the action of said vibration so that, by this oscillating rotation, said resonator means generates an antivibration inertia force which opposes said vibration and thus reduces its transmission from one body to the other. PA1 of breakage of one or more leaves, the only consequence is a drop in the reduction of vibration and therefore an increase in its transmission from one body to the other; and PA1 of breakage of the annular element, the resonator means comes into abutment between said bodies, and this maintains a connection between the latter and does not influence the operation of the system comprising them. PA1 two masses arranged symmetrically with respect to the center of said annular element, which makes it possible to simplify production; or PA1 two masses arranged on one same side of a plane of symmetry of said annular element passing roughly through the center of the zones where the latter is attached to said bodies, which makes it possible to free up the opposite side and thus reduce the size on this opposite side; or PA1 four masses arranged symmetrically in pairs: PA1 in a first embodiment, in that at least some of said support bars are formed of two sections and in that said suspension device comprises, for each of the support bars thus formed, an antivibration device according to the invention, which is arranged between said sections of the support bar; and PA1 in a second embodiment, in that it additionally comprises, for each of at least some of said support bars, an antivibration device according to the invention, which is arranged at one end of the corresponding bar and which is intended to reduce the transmission of vibration between this bar and the element (the transmission gearbox or the fuselage for example) to which this end of the bar is connected. PA1 owing to the integration of the antivibration device into the support bars or pieces and therefore to the absence of mass supports and beating masses between the transmission gearbox and the support pieces, the size of said suspension device is reduced and its accessibility is improved; and PA1 the cost is reduced, particularly as a result of the absence of expensive elastomer articulations which exist, in particular, in the mounting of the suspension leaves and mass supports of these known suspension devices.
Although particularly effective, said known uspension device does have certain drawbacks, particularly:
Document U.S. Pat. No. 4,781,363 discloses an antivibration device which can be mounted between the main transmission gearbox and the fuselage of a helicopter, to reduce the transmission of vibration between the two.
To this end, this known antivibration device comprises:
In addition, when the rigidity of the deformable chambers is not great enough to withstand the effects of the vibration, said known device may additionally comprise a resistant elastic element of circular shape, made of a glass-fiber reinforced plastic.
This known device thus allows certain drawbacks of the aforementioned suspension device to be overcome, and in particular makes it possible to reduce the size.
However, this known antivibration device also has a great many drawbacks, and in particular: